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Software Engineering
Saeed Akhtar
The University of Lahore
Lecture 4Originally shared fo
r:
mashhoood.webs.com
Review of Last LectureWhen Waterfall model is used?Advantages and Disadvantages of Waterfall
model?What are the steps in CBSE?Pros and cons of CBSE?How Incremental Model Works?Advantages and disadvantages of
Incremental Model?
Objectives
Spiral Model
RAD Model
Prototype Model
Spiral Model
Process is represented as a spiral rather than as a sequence of activities
Each loop in the spiral represents a phase in the process.
No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required.
Risks are explicitly assessed and resolved throughout the process.
Spiral model sectors
Objective setting Specific objectives for the phase are identified.
Risk assessment and reduction Risks are assessed and activities put in place to
reduce the key risks.Development and validation
A development model for the system is chosen which can be any of the generic models.
Planning The project is reviewed and the next phase of the
spiral is planned.
Advantages of Spiral Model
Estimates (budget, schedule) become more realistic
It is more able to cope with the (nearly inevitable) changes
Software engineers (who can get restless with protracted design processes) can get their hands in
Disadvantages of Spiral ModelLimiting re-usability
Applied differently for each application
Requires considerable expertise in risk evaluation and reduction
Risk assessment could cost more than development
When to use Spiral Model When creation of a prototype is appropriate
When costs and risk evaluation is important
Users are unsure of their needs
Significant changes are expected
Difference b/w Waterfall and Spiral Model
Risk Factor
Requirements are freezed
Linear sequential and Loop
Spiral Model is costly
better communication between developer and customer
RAD Model
Requirements planning phase
User description phase
Construction phase
Cutover phase
RAD Model Strengths Time-box approach mitigates cost and
schedule risk
Reduced cycle time and improved productivity
Customer involved throughout
Focus moves from documentation to code
RAD Weaknesses
Must give quick responses
Never achieving closure
Hard to use with legacy systems
When to use RAD Modelwell-known requirements
User involved throughout the life cycle
Project can be time-boxed
Functionality delivered in increments
High performance not required
Waterfall Model Vs RAD ModelHow big is the project?Do you need a prototype?Are you using a packaged solution?How flexible is your team?How much will your customer participate in
the process?Is your project manager experienced?
Prototyping ModelDevelopers build a prototype during the requirements
phase
Prototype is evaluated by end users
Users give corrective feedback
Developers further refine the prototype
When the user is satisfied, the prototype code is brought up to the standards needed for a final product.
Advantages of Prototyping ModelCustomers can “see” the system requirements
Developers learn from customers
A more accurate end product
Unexpected requirements accommodated
Allows for flexible design and development
Drawbacks of Prototyping ModelBad reputation for “quick-and-dirty” methods
Maintainability may be overlooked
The customer may want the prototype delivered
Process may continue forever
Prototyping Model
Thank You